778 



THE NERVOUS SYSTEM 



Nerccs 

 Fourth thoracic (A) Just below upper border of spine of first thoracic vertebra. 



(B) Junction of upper third and lower two-thirds of spine of third thonicic 

 vertebra. 

 Fifth . . (A) Tapper border of si)ine of second thoracic vertebra. 



(B) Junction of upper quarter and lower three-quarters of spine of fourtli 

 thoracic vertebra. 

 Sixth ., (A) Lower border of spine of second thoracic vertebra. 



(B) Just below upper border of spine of fifth thoracic vertebra. 

 Seventh ., (A) Junction of upper third and lower two-thirds of spine of fourth thoracic 



vertebra. 

 (B) Just above lower border of spine of fifth thoracic vertebra. 

 Eighth ,, (A) Junction of upper two-thirds and lower third of interval between spines 



of fourth thoracic and fifth thoracic vertebrae. 

 (B) Junction of upper quarter and lower three-quarters of spine of sixth 

 thoracic vertebra. 

 Ninth ,, (A) Midway between spines of fifth thoracic and sixth thoracic vertebra. 



(B) Upper border of spine of seventh thoracic vertebra. 

 Tenth ,, (A) Midway between spines of sixth thoracic and seventh thoracic vertebrae. 



(B) Middle of spine of eighth thoracic vertebra. 

 Eleventh ,, (A) Junction of upper quarter and lower three-quarters of spine of seventh 



thoracic vertebra. 

 (B) Just above spine of ninth thoracic vertebra. 

 Twelfth ,, (A) Junction of upper quarter and lower three-quarters of spine of eighth 



thoracic vertebra. 

 (B) Just below spine of ninth thoracic vertebra. 

 First lumbar (A) Midway between spines of eighth thoracic and ninth thoracic vertebrae. 



(B) Lower border of spine of tenth thoracic vertebra. 

 Second ,, (A) Middle of spine of ninth thoracic vertebra. 



(B) Junction of upper third and lower two-thirds of spine of eleventh thoracic 

 vertebra. 

 Third ,, (A) Middle of spine of tenth thoracic vertebra. 



(B) Just below spine of eleventh thoracic vertebra. 

 Fourth ,, (A) Just below spine of tenth thoracic vertebra. 



(B) Junction of upper quarter and lower tlu'ee-quarters of spine of twelfth 

 thoracic vertebra. 

 Fifth ,, (A) Junction of upper third and lower two-thirds of spine of eleventh thoracic 



vertebra. 

 (B) Middle of spine of twelfth thoracic vertebra. 

 First sacral (A) Just above lower border of spine of eleventh thoracic vertebra. 

 Fifth ,, (B) Lower border of spine of first lumbar vertebra. 



Coccygeal (A) Lower border of spine of first lumbar vertebra. 



(B) Just below upper border of spine of second lumbar vertebra. 



Classification and number. — There are thirty-one pairs of spinal nerves, viz. — 

 eight cervical, twelve tlioracic, five lumbar, five sacral, and one cocc3'geal nerve. The 

 cervical nerves are named from the vertebrae below them; the thoracic, lumbar, 

 sacral and coccygeal nerves from the vertebrae above them. The first cervical or 

 suboccipital nerve escapes through the interval l)etween the occipital bone and the 

 atlas; the eighth cervical passes through the intervertebral foramen between the 

 seventh cervical and first thoracic vertebrae. 



General distribution. — Each spinal nerve, at its exit from the intervertebral 

 foramen, gives a small recurrent branch (Luschka), which receives a communicat- 

 ing twig from the sympathetic, and re-enters the neural canal to be distributed to 

 the meninges and blood-vessels Avithin the canal. Innnediately after its exit eacli 

 nerve divides into an anterior and a posterior primary division. Botli the anterior 

 and posterior ]irimary divisions are mixed nerves, containing fibres derived from 

 both the anterior and tlie posterior roots. 



The posterior primary divisions are, with two exceptions, smaller than the 

 anterior divisions. The posterior divisions of the first and second cervical nerves 

 are larger than the anterior; that of the second cervical nerve being three or four 

 times as large as the anterior division. In the regions of the great plexuses 

 (brachial, lumbar, and sacral) the anterior division is very much larger than the 



